L I G 
which arc diftinguifhed by the curious in botany ; 
but as they are plants- of no ufe, I (hall hot enumerate 
them. 
The fecond fort (which is fifed to cure the bite of mad 
dogs) grows on commons and open heaths* where the 
Grafs is ihorc* and the ground alrnoft bare, in moft 
parts of England,, efpecially on declivities, arid on the 
fides of pits. This fpreads on the furface of the 
ground, and, when in perfedion, is of an Afh-co- 
lour, but as it grows old, it alters, and becomes of a 
dark colour. This is often carried into gardens 
with the turf which is laid for walks and dopes, and 
where the foil is , moift and cool, it will fpread, 
and be difficult to deftroy, fo that it renders the 
Grafs unfighdy * but this is the only method yet 
known to have it grow in gardens, where it is defired. 
This is efteemed a fovereign remedy for the bite of 
tnad dogs* and hath been for many years ufed \yith 
great fuccefs. It was communicated to the Royal So- 
ciety by Mr. George Dampier, whofe uncle had long 
tiled this plant, to cure the bite of mad dogs on men 
and animals, With infallible fuccefs. The method of 
taking it he has delivered as followeth : 44 Take of the 
Ci herb, and dry it either in an oven, by the fire, or 
44 in the fun then powder it, and pafs it through a 
64 fine fieve mix this vfith an equal quantity of fine 
44 powdered pepper. The common dofe of this mix- 
44 tiife is four fcruples, which may be taken in warm 
ie milk, beer, ale, or broth.” He alfo advifes* that 
the part bitten be well wafhed* as alfo the clothes of 
the perfon who was bit, left any of the fnivel, or dri- 
vel of the mad dog fhould remain. If the perfon bit- 
ten be full grown, he advifes, that he be blooded be- 
fore the medicine is taken, and to ufe the remedy as 
foon after the bite as poflible, as alfo to repeat the 
dofe two or three feveral mornings falling. 
LIGHT is ufed in various fenfes: i. Sometimes it 
fignifies that fenfation which is occafioned in the mind 
by the view of luminous bodies; 
2. For thofe properties in thofe bodies, whereby they 
are fitted to excite thofe fenlations in us. 
2. A certain adion of the luminous body on the me- 
dium between that and the eye, by the means of 
which the one is fuppofed to ad on the other, and this 
is called feeondary Light, or derived Light, in diftinc- 
tion to that of luminous bodies, which is called pri- 
mary or innate Light. 
As to the phenomenon of light, philofophers have 
explained it leveral ways * Ariftotle by fuppofmg fome 
bodies to be tranfparent, as air, water, ice, &c, The 
Cartefians have confiderably refined upon this notion 
of Light, and own, that Light, as it exifts in the lu- 
minous body, is nothing elfe but a power or faculty 
of exciting in us a very clear and vivid fenfation * and 
Father Malebranche explains the nature of Light by 
a fuppofed analogy between it and found, the latter 
of which is allowed to be produced by the lhaking 
or vibration of the infenfible parts of the fonorous 
body. 
But the greateft difcovertes into this wonderful phe- 
nomenon have been made by Sir Ifaac Newton, that 
the primary light confifts wholly in a certain motion 
of the particles of the lucid body, whereby they do 
not propel any fiditious matter fuppofed to be lodged 
in the hidden pores of tranfparent bodies, but throw 
off from the luminous body certain very fmall parti- 
cles, which are emitted every way with great force. 
Arid the feeondary or derived Light, not in a cona- 
tus, but in a real motion of thefe particles receding 
every way from the luminous body in right lines, and 
with an incredible velocity. 
For it has been demonftrated by Mr. Reaumur, from 
the obfervation on the fatellites of Jupiter, that the 
progrefs of Light from the fun to our earth is not 
above ten minutes, and therefore, fince the earth is 
at leaft 10,000 of its own diameters diftant from the 
fan. Light muft run 10,000 of thofe diameters in a 
minute, which is above 100,000 miles in a fecond. 
And if a bullet, moving with the fame celerity with 
which it leaves the muzzle of a cannon, requires 
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twenty-five years to pafs from the earth to the fun,, as 
Mr. Huygens has computed * then the velocity of 
Light will be to that of a cannon ball, as twenty-five 
years is .to ten minutes, which is above 10,000 to 1 : 
fo that the particles of Light move above a million 
of times fwifter than a cannon ball, from which ra- 
pidity of motion very ftrange effeds may be pro- 
duced •, but Sir Ifaac Newton has ftiewn, paft con- 
tradiction, that the Light of the fun is near feven mi- 
nutes in its paffage to the earth, which is the fpace of 
50,000,000, a velocity 10,000,000 times greater than 
that wherewith a ball flies out of the mouth of a 
cannon. 
Sir Ifaac Newton alfo obfervfes, that bodies and Light 
ad mutually on one another : bodies on Light, in 
emitting, reflexing, refrading, and infleding it, and 
Light on bodies, by heating them, and putting their 
parts into a vibrating motion, wherein heat principally 
confifts ; for he obferves, that all fixed bodies, when 
heated beyond a certain degree, emit Light and fhine, 
which fhining, &c. appears to be owing to the vi- 
brating motion of the parts, and all bodies abounding 
in earthy and fulphureous particles, if they be fuffi- 
ciently agitated emit Light, which way foever the 
agitation be effeded. 
The fame great author obferves, that there are but 
three affedions of Light wherein the rays differ, viz. 
refrangibility, reflexibility, and colour * and thofe rays 
which agree in refrangibility, agree alfo in the other 
two, whence they may be well defined homogeneaL 
Again, the colours exhibited by homogeneal Lights 
he calls homogeneal colours, and thofe produced by 
heterogeneal Light, heterogeneal colours* from which 
definitions he advances feveral propofitions : 
1. That the fun’s Light confifts of rays differing by 
indefinite degrees of refrangibility. 
2. That rays, which differ in refrangibility, when 
parted from one another, do proportionably differ ift 
the colours which they exhibit. 
3. That there are as many Ample and homogeneal 
colours, as there are degrees of refrangibility, for tot 
every degreeof refrangibility belongs adifferentcolour. 
4. Whitenefs, in all refpeds, like that of the fun’s 
immediate Light, and of all the ufual objeds of our 
fenfes, cannot be compounded of Ample colours, with- 
out an indefinite variety of them, for to fuch a com- 
pofition there are required rays endued with all the in- 
definite degrees of refrangibility, which infer as many 
Ample colours. 
5. The rays of Light do not a6t one on another in 
pafling through the fame medium. 
6. The rays of Light do not fuffer any alteration of 
their qualities from refradion, nof from the adjacent 
quiefeent medium. 
7. There can be no homogeneal colours produced 
out of Light by refradion, which are nqt commixed 
in it before, fince refradion changes not the qualities 
of the rays, but only feparates thofe that have divers 
qualities by means of their different refrangibility. 
8. The fun’s Light is an aggregate of homogeneal 
colours, whence homogeneal colours may be called 
primitive or original. 
Hence proceeds the whole theory of colours in plants 
and flowers. 
Thofe parts, v. g. which are the moft refrangible, 
conftitute Violet colour, the dimmeft and moft lan- 
guid of all colours. 
And, on the contrary, thofe particles that are the 
leaft refrangible, conftitute a ray or a red colour, 
which is the brighteft and moft vivid of all colours 5 
the other particles being diftinguifhed into little rays* 
according to their refpedive magnitudes and degrees 
of refrangibility, excite intermediate vibrations, and 
fo occafion the fenfations of the intermediate colours. 
See Sir Ifaac Newton’s Dodrine of Colours. 
Perhaps thefe obfervations of Light may to fome 
perfons feem foreign to the fubjed matter of this 
book, yet, if thoroughly underftood might probably 
be found very ufeful. The learned and curious en- 
quirer into the bufmefs of vegetation, the Rev. Dr. 
M Hales, 
